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147
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149
150<div class="main">
151
152
153
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]154<p class="navigation-index">[<a href="#overview">Architecture Overview</a> &bull; <a href="#cache">The Pixel Cache</a> &bull; <a href="#stream">Streaming Pixels</a> &bull; <a href="#properties">Image Properties and Profiles</a> &bull; <a href="#tera-pixel">Large Image Support</a> &bull; <a href="#threads">Threads of Execution</a> &bull; <a href="#distributed">Heterogeneous Distributed Processing</a> &bull; <a href="#coders">Custom Image Coders</a> &bull; <a href="#filters">Custom Image Filters</a>]</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]155
156<div class="doc-section">
157<p>The citizens of Oz were quite content with their benefactor, the all-powerful Wizard. They accepted his wisdom and benevolence without ever questioning the who, why, and where of his power. Like the citizens of Oz, if you feel comfortable that ImageMagick can help you convert, edit, or compose your images without knowing what goes on behind the curtain, feel free to skip this section. However, if you want to know more about the software and algorithms behind ImageMagick, read on. To fully benefit from this discussion, you should be comfortable with image nomenclature and be familiar with computer programming.</p>
158</div>
159
160<h2><a name="overview"></a>Architecture Overview</h2>
161<div class="doc-section">
162
163<p>An image typically consists of a rectangular region of pixels and metadata. To convert, edit, or compose an image in an efficient manner we need convenient access to any pixel anywhere within the region (and sometimes outside the region). And in the case of an image sequence, we need access to any pixel of any region of any image in the sequence. However, there are hundreds of image formats such JPEG, TIFF, PNG, GIF, etc., that makes it difficult to access pixels on demand. Within these formats we find differences in:</p>
164
165<ul>
166 <li>colorspace (e.g RGB, CMYK, YUV, Lab, etc.)</li>
167 <li>bit depth (.e.g 1, 4, 8, 12, 16, etc.)</li>
168 <li>storage format (e.g. unsigned, signed, float, double, etc.)</li>
169 <li>compression (e.g. uncompressed, RLE, Zip, BZip, etc.)</li>
170 <li>orientation (i.e. top-to-bottom, right-to-left, etc.),</li>
171 <li>layout (.e.g. raw, interspersed with opcodes, etc.)</li>
172</ul>
173
174<p>In addition, some image pixels may require attenuation, some formats permit more than one frame, and some formats contain vector graphics that must first be rasterized (converted from vector to pixels).</p>
175
176<p>An efficient implementation of an image processing algorithm may require we get or set:</p>
177
178<ul>
179 <li>one pixel a time (e.g. pixel at location 10,3)</li>
180 <li>a single scanline (e.g. all pixels from row 4)</li>
181 <li>a few scanlines at once (e.g. pixel rows 4-7)</li>
182 <li>a single column or columns of pixels (e.g. all pixels from column 11)</li>
183 <li>an arbitrary region of pixels from the image (e.g. pixels defined at 10,7 to 10,19)</li>
184 <li>a pixel in random order (e.g. pixel at 14,15 and 640,480)</li>
185 <li>pixels from two different images (e.g. pixel at 5,1 from image 1 and pixel at 5,1 from image 2)</li>
186 <li>pixels outside the boundaries of the image (e.g. pixel at -1,-3)</li>
187 <li>a pixel component that is unsigned or in a floating-point representation (e.g. 0.17836)</li>
188 <li>a high-dynamic range pixel that can include negative values as well as values that exceed the quantum depth (e.g. -0.00716)</li>
189 <li>one or more pixels simultaneously in different threads of execution</li>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]190 <li>all the pixels in memory to take advantage of speed-ups offered by executing in concert across heterogeneous platforms consisting of CPUs, GPUs, and other processors</li>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]191</ul>
192
193<p>In addition, some images include a clip mask that define which pixels are eligible to be updated. Pixels outside the area defined by the clip mask remain untouched.</p>
194
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]195<p>Given the varied image formats and image processing requirements, we implemented the ImageMagick <a href="#cache">pixel cache</a> to provide convenient sequential or parallel access to any pixel on demand anywhere inside the image region (we call these <a href="#authentic-pixels">authentic pixels</a>) and from any image in a sequence. In addition, the pixel cache permits access to pixels outside the boundaries defined by the image (we call these <a href="#virtual-pixels">virtual pixels</a>).</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]196
197<p>In addition to pixels, images have a plethora of <a href="#properties">image properties and profiles</a>. Properties include the well known items such as width, height, depth, and colorspace. An image may have optional properties which might include the image author, a comment, a create date, and others. Some images also include profiles for color management, or EXIF, IPTC, 8BIM, or XMP informational profiles. ImageMagick provides command line options and programming methods to get, set, or view image properties or profiles or apply profiles.</p>
198
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]199<p>ImageMagick consists of more than 400,000 lines of C code and optionally depends on several million lines of code in dependent libraries (e.g. JPEG, PNG, TIFF libraries). Given that, one might expect a huge architecture document. However, a great majority of image processing is simply accessing pixels and its metadata and our simple and elegant implementation makes this easy for the ImageMagick developer. We discuss the implementation of the pixel cache and getting and setting image properties and profiles in the next few sections. Next, we discuss using ImageMagick within a <a href="#threads">thread</a> of execution. In the final sections, we discuss <a href="#coders">image coders</a> to read or write a particular image format followed by a few words on creating a <a href="#filters">filter</a> to access or update pixels based on your custom requirements.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]200
201</div>
202
203<h2><a name="cache"></a>The Pixel Cache</h2>
204<div class="doc-section">
205
206<p>The ImageMagick pixel cache is a repository for image pixels with up to 5 channels. The first 4 channels are stored contiguously and an optional second area follows with 1 channel. The channels are at the depth specified when ImageMagick was built. The channel depths are 8 bits-per-pixel component for the Q8 version of ImageMagick, 16 bits-per-pixel component for the Q16 version, and 32 bits-per-pixel component for the Q32 version. By default pixel components are unsigned quantities, however, if you use the <a href="../www/high-dynamic-range.html">high dynamic-range</a> version of ImageMagick, the components are 32-bit floating point. The primary 4 channels can hold any value but typically contain red, green, blue, and alpha intensities or cyan, magenta, yellow, and alpha intensities. The optional fifth channel contains the colormap indexes for colormapped images or the black channel for CMYK images. The pixel cache storage may be heap memory, anonymous memory mapped memory, disk-backed memory mapped, or on disk. The pixel cache is reference-counted. Only the cache properties are copied when the cache is cloned. The cache pixels are subsequently copied when you signal your intention to update any of the pixels.</p>
207
208<h3>Create the Pixel Cache</h3>
209<div class="doc-section">
210
211<p>The pixel cache is associated with an image when it is created and it is initialized when you try to get or put pixels. Here are three common methods to associate a pixel cache with an image:</p>
212
213<h4>Create an image canvas initialized to the background color:</h4>
214<p class="code">
215 image=AllocateImage(image_info);
216 if (SetImageExtent(image,640,480) == MagickFalse)
217 { /* an exception was thrown */ }
218 (void) QueryMagickColor("red",&amp;image-&gt;background_color,&amp;image-&gt;exception);
219 SetImageBackgroundColor(image);
220</p>
221
222<h4>Create an image from a JPEG image on disk:</h4>
223<p class="code"> (void) strcpy(image_info-&gt;filename,"image.jpg"):
224 image=ReadImage(image_info,exception);
225 if (image == (Image *) NULL)
226 { /* an exception was thrown */ }
227</p>
228<h4>Create an image from a memory based image:</h4>
229<p class="code">
230 image=BlobToImage(blob_info,blob,extent,exception);
231 if (image == (Image *) NULL)
232 { /* an exception was thrown */ }
233</p>
234
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]235<p>In our discussion of the pixel cache, we use the <a href="../www/magick-core.html">MagickCore API</a> to illustrate our points, however, the principles are the same for other program interfaces to ImageMagick.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]236
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]237<p>When the pixel cache is initialized, pixels are scaled from whatever bit depth they originated from to that required by the pixel cache. For example, a 1-channel 1-bit monochrome PBM image is scaled to a 4 channel 8-bit RGBA image, if you are using the Q8 version of ImageMagick, and 16-bit RGBA for the Q16 version. You can determine which version you have with the <a href="../www/command-line-options.html#version">&#x2011;version</a> option: </p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]238
cristye4cbe742010-02-18 22:19:38 +0000[diff] [blame]239<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Version: ImageMagick 6.5.9-8 2010-02-15 Q16 http://www.imagemagick.org</span></p>
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]240<p>As you can see, the convenience of the pixel cache sometimes comes with a trade-off in storage (e.g. storing a 1-bit monochrome image as 16-bit RGBA is wasteful) and speed (i.e. storing the entire image in memory is generally slower than accessing one scanline of pixels at a time). In most cases, the benefits of the pixel cache typically outweigh any disadvantages.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]241</div>
242
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]243<h3><a name="authentic-pixels"></a>Access the Pixel Cache</h3>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]244<div class="doc-section">
245
246<p>Once the pixel cache is associated with an image, you typically want to get, update, or put pixels into it. We refer to pixels inside the image region as <em>authentic pixels</em> and outside the region as <em>virtual pixels</em>. Use these methods to access the pixels in the cache:</p>
247<ul>
248 <li><a href="../www/api/cache.html#GetVirtualPixels">GetVirtualPixels()</a> gets pixels that you do not intend to modify</li>
249 <li><a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> gets pixels that you intend to modify</li>
250 <li><a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> queue pixels that you intend to modify</li>
251 <li><a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> update the pixel cache with any modified pixels</li>
252</ul>
253
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]254<p>Here is a typical <a href="../www/magick-core.html">MagickCore</a> code snippet for manipulating pixels in the pixel cache. In our example, we copy pixels from the input image to the output image and decrease the intensity by 10%:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]255
256<div class="viewport">
257<pre class="code">
258 long
259 x,
260 y;
261
262 const PixelPacket
263 *p;
264
265 PixelPacket
266 *q;
267
268 destination=CloneImage(source,source->columns,source->rows,MagickTrue,exception);
269 if (destination == (Image *) NULL)
270 { /* an exception was thrown */ }
271 for (y=0; y &lt; (long) source-&gt;rows; y++)
272 {
273 p=GetVirtualPixels(source,0,y,source-&gt;columns,1,exception);
274 q=GetAuthenticPixels(destination,0,y,destination-&gt;columns,1,exception);
275 if ((p == (const PixelPacket *) NULL) || (q == (PixelPacket *) NULL)
276 break;
277 for (x=0; x &lt; (long) source-&gt;columns; x++)
278 {
279 q-&gt;red=90*p-&gt;red/100;
280 q-&gt;green=90*p-&gt;green/100;
281 q-&gt;blue=90*p-&gt;blue/100;
282 q-&gt;opacity=90*p-&gt;opacity/100;
283 p++;
284 q++;
285 }
286 if (SyncAuthenticPixels(destination,exception) == MagickFalse)
287 break;
288 }
289 if (y &lt; (long) source-&gt;rows)
290 { /* an exception was thrown */ }
291</pre>
292</div>
293
294<p>When we first create the destination image by cloning the source image, the pixel cache pixels are not copied. They are only copied when you signal your intentions to modify the pixel cache by calling <a href="../www/api/cache.html#GetAuthenticPixels">GetAuthenticPixels()</a> or <a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a>. Use <a href="../www/api/cache.html#QueueAuthenticPixels">QueueAuthenticPixels()</a> if you want to set new pixel values rather than update existing ones. Finally, use <a href="../www/api/cache.html#SyncAuthenticPixels">SyncAuthenticPixels()</a> to ensure any updated pixels are pushed to the pixel cache.</p>
295
296<p>Recall how we mentioned that the indexes of a colormapped image or the black channel of a CMYK image are stored separately. Use <a href="../www/api/cache.html#GetVirtualIndexes">GetVirtualIndexes()</a> (to read the indexes) or <a href="../www/api/cache.html#GetAuthenticIndexes">GetAuthenticIndexes()</a> (to update the indexes) to gain access to this channel. For example, to print the colormap indexes, use:</p>
297
298<pre class="code">
299 const IndexPacket
300 *indexes;
301
302 for (y=0; y &lt; (long) source-&gt;rows; y++)
303 {
304 p=GetVirtualPixels(source,0,y,source-&gt;columns,1);
305 if (p == (const PixelPacket *) NULL)
306 break;
307 indexes=GetVirtualIndexes(source);
308 for (x=0; x &lt; (long) source-&gt;columns; x++)
309 (void) printf("%d\n",indexes[x];
310 }
311 if (y &lt; (long) source-&gt;rows)
312 /* an exception was thrown */
313</pre>
314
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]315<p>The pixel cache manager decides whether to give you direct or indirect access to the image pixels. In some cases the pixels are staged to an intermediate buffer-- and that is why you must call SyncAuthenticPixels() to ensure this buffer is <em>pushed</em> out to the pixel cache to guarantee the corresponding pixels in the cache are updated. For this reason we recommend that you only read or update a scanline or a few scanlines of pixels at a time. However, you can get any rectangular region of pixels you want. GetAuthenticPixels() requires that the region you request is within the bounds of the image area. For a 640 by 480 image, you can get a scanline of 640 pixels at row 479 but if you ask for a scanline at row 480, an exception is returned (rows are numbered starting at 0). GetVirtualPixels() does not have this constraint. For example,</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]316
317<pre class="code">
318 p=GetVirtualPixels(source,-3,3,source-&gt;columns+7,7,exception);
319</pre>
320
321<p>gives you the pixels you asked for without complaint, even though some are not within the confines of the image region.</p>
322</div>
323
324<h3><a name="virtual-pixels"></a>Virtual Pixels</h3>
325<div class="doc-section">
326
327 <p>Access to the virtual pixels are controlled by the <a href="../www/api/cache.html#SetImageVirtualPixelMethod">SetImageVirtualPixelMethod()</a> method from the MagickCore API or the <a href="../www/command-line-options.html#virtual-pixel">&#x2011;virtual&#x2011;pixel</a> option from the command line. The methods include:</p>
328
329<pre class="text">
330 background: the area surrounding the image is the background color
331 black: the area surrounding the image is black
332 checker-tile: alternate squares with image and background color
333 dither: non-random 32x32 dithered pattern
334 edge: extend the edge pixel toward infinity
335 gray: the area surrounding the image is gray
336 horizontal-tile: horizontally tile the image, background color above/below
337 horizontal-tile-edge: horizontally tile the image and replicate the side edge pixels
338 mirror: mirror tile the image
339 random: choose a random pixel from the image
340 tile: tile the image (default)
341 transparent: the area surrounding the image is transparent blackness
342 vertical-tile: vertically tile the image, sides are background color
343 vertical-tile-edge: vertically tile the image and replicate the side edge pixels
344 white: the area surrounding the image is white
345</pre>
346
347<p>There is a plethora of image processing algorithms that require a neighborhood of pixels about a pixel of interest. There is typically a caveat concerning how to handle pixels around the image boundaries, known as edge pixels. With virtual pixels, you do not need to concern yourself about special edge processing other than choosing which virtual pixel method is most appropriate for your algorithm.</p>
348</div>
349
350<h3>Cache Storage and Resource Requirements</h3>
351<div class="doc-section">
352
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]353<p>Recall that this simple and elegant design of the ImageMagick pixel cache comes at a cost in terms of storage and processing speed. The pixel cache storage requirements scales with the area of the image and the bit depth of the pixel components. For example, if we have a 640 by 480 image and we are using the Q16 version of ImageMagick, the pixel cache consumes image <em>width * height * bit-depth / 8 * channels</em> bytes or approximately 2.3 mebibytes (i.e. 640 * 480 * 2 * 4). Not too bad, but what if your image is 25000 by 25000 pixels? The pixel cache requires approximately 4.7 gibibytes of storage. Ouch. ImageMagick accounts for possible huge storage requirements by caching large images to disk rather than memory. Typically the pixel cache is stored in memory using heap memory. If heap memory is exhausted, pixels are stored in in an anonymous map; if the anonymous memory map is exhausted, we create the pixel cache on disk and attempt to memory-map it; and if memory-map memory is exhausted, we simply use standard disk I/O. Disk storage is cheap but it is also very slow, upwards of 1000 times slower than memory. We can get some speed improvements, up to 5 times, if we use memory mapping to the disk-based cache. These decisions about storage are made <em>automagically</em> by the pixel cache manager negotiating with the operating system. However, you can influence how the pixel cache manager allocates the pixel cache with <em>cache resource limits</em>. The limits include:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]354
355<dl class="doc">
356 <dt class="doc">files</dt>
357 <dd>maximum number of open pixel cache files. When this limit is exceeded, any subsequent pixels cached to disk are closed and reopened on demand. This behavior permits a large number of images to be accessed simultaneously on disk, but with a speed penalty due to repeated open/close calls.</dd>
358 <dt class="doc">area</dt>
359 <dd>maximum area in bytes of any one image that can reside in the pixel cache memory. If this limit is exceeded, the image is automagically cached to disk.</dd>
360 <dt class="doc">memory</dt>
361 <dd>maximum amount of memory in bytes to allocate for the pixel cache from the anonymous mapped memory or the heap.</dd>
362 <dt class="doc">map</dt>
363 <dd>maximum amount of memory map in bytes to allocate for the pixel cache.</dd>
364 <dt class="doc">disk</dt>
365 <dd>maximum amount of disk space in bytes permitted for use by the pixel cache. If this limit is exceeded, the pixel cache is not created and a fatal exception is thrown.</dd>
366</dl>
367
368<p>To determine the current setting of these limits, use this command:</p>
369
cristyc1c61662009-09-30 14:04:37 +0000[diff] [blame]370<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -list resource</span><span class='crtout'><pre>File Area Memory Map Disk Thread Time
371------------------------------------------------------------------------
372 768 11.551GiB 8.6631GiB 23.102GiB 16EiB 8 unlimited</pre></span></p>
373<p>You can set these limits either with <a href="../www/resources.html#environment">environment variables</a>, the <a href="../www/command-line-options.html#limit">-limit</a> command line option, or the <a href="../www/api/resource.html#SetMagickResourceLimit">SetMagickResourceLimit()</a> MagickCore API method. As an example, our online web interface to ImageMagick, <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">ImageMagick Studio</a>, has an area limit of 64 mebibytes, a memory limit of 128 mebibytes and a map limit of 256 mebibytes and a disk limit of 1 gibibytes. Since we process multiple simultaneous sessions, we don't want any one session consuming all the available memory. Instead large images are cached to disk. If the image is too large and exceeds the pixel cache disk limit, the program exits. In addition, we place a 60 second time limit to prevent any run-away processing tasks.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]374
375<p>Note, the cache limits are global, meaning if you create several images, the combined resource requirements are compared to the limit to determine the pixel cache storage disposition.</p>
376</div>
377
378<h3>Cache Views</h3>
379<div class="doc-section">
380
381<p>GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), and SyncAuthenticPixels() from the MagickCore API can only deal with one pixel cache area per image at a time. Suppose you want to access the first and last scanline from the same image at the same time? The solution is to use a <em>cache view</em>. A cache view permits you to access as many areas simultaneously in the pixel cache as you require. The cache view <a href="../www/api/cache-view.html">methods</a> behave like the previous methods except you must first open a view and close it when you are finished with it. Here is a snippet of MagickCore code that permits us to access two areas of an image simultaneously:</p>
382
383<pre class="code">
384 CacheView
385 *view_1,
386 *view_2;
387
388 view_1=OpenCacheView(source);
389 view_2=OpenCacheView(source);
390 for (y=0; y &lt; (long) source-&gt;rows; y++)
391 {
392 u=GetCacheViewVirtualPixels(view_1,0,y,source-&gt;columns,1,exception);
393 v=GetCacheViewVirtualPixels(view_2,0,source-&gt;rows-y-1,source-&gt;columns,1,exception);
394 if ((u == (const PixelPacket *) NULL) || (v == (const PixelPacket *) NULL))
395 break;
396 for (x=0; x &lt; (long) source-&gt;columns; x++)
397 {
398 /* do something with u &amp; v here */
399 }
400 }
401 view_1=CloseCacheView(view_1);
402 view_2=CloseCacheView(view_2);
403 if (y &lt; (long) source-&gt;rows)
404 { /* an exception was thrown */ }
405</pre>
406</div>
407
408<h3>Magick Persistent Cache Format</h3>
409<div class="doc-section">
410
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]411<p>Recall that each image format is decoded by ImageMagick and the pixels are deposited in the pixel cache. If you write an image, the pixels are read from the pixel cache and encoded as required by the format you are writing (e.g. GIF, PNG, etc.). The Magick Persistent Cache (MPC) format is designed to eliminate the overhead of decoding and encoding pixels to and from an image format. MPC writes two files. One, with the extension <kbd>.mpc</kbd>, retains all the properties associated with the image or image sequence (e.g. width, height, colorspace, etc.) and the second, with the extension <kbd>.cache</kbd>, is the pixel cache in the native raw format. When reading an MPC image file, ImageMagick reads the image properties and memory maps the pixel cache on disk eliminating the need for decoding the image pixels. The tradeoff is in disk space. MPC is generally larger in file size than most other image formats.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]412</div>
413
414<h3>Best Practices</h3>
415<div class="doc-section">
416
417<p>Although you can request any pixel from the pixel cache, any block of pixels, any scanline, multiple scanlines, any row, or multiple rows with the GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels, GetCacheViewVirtualPixels(), GetCacheViewAuthenticPixels(), and QueueCacheViewAuthenticPixels() methods, ImageMagick is optimized to return a few pixels or a few pixels rows at time. There are additional optimizations if you request a single scanline or a few scanlines at a time. These methods also permit random access to the pixel cache, however, ImageMagick is optimized for sequential access.</p>
418
419<p>If you update pixels returned from GetAuthenticPixels() or GetCacheViewAuthenticPixels(), don't forget to call SyncAuthenticPixels() or SyncCacheViewAuthenticPixels() respectively to ensure your changes are synchronized with the pixel cache.</p>
420
421<p>Use QueueAuthenticPixels() or QueueCacheViewAuthenticPixels() if you are setting an initial pixel value. The GetAuthenticPixels() or GetCacheViewAuthenticPixels() method reads pixels from the cache and if you are setting an initial pixel value, this read is unnecessary. Don't forget to call SyncAuthenticPixels() or SyncCacheViewAuthenticPixels() respectively to push your updates to the pixel cache.</p>
422
423<p>GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), and SyncAuthenticPixels() are slightly more efficient than their cache view counter-parts. However, cache views are required if you need access to more than one region of the image simultaneously or if more than one <a href="#threads">thread of execution</a> is accessing the image.</p>
424
425<p>You can request pixels outside the bounds of the image with GetVirtualPixels() or GetCacheViewVirtualPixels(), however, it is more efficient to request pixels within the confines of the image region.</p>
426
427<p>Although you can force the pixel cache to disk using appropriate resource limits, disk access can be upwards of 1000 times slower than memory access. For fast, efficient, access to the pixel cache, try to keep the pixel cache in heap memory or anonymous mapped memory.</p>
428
429<p>The ImageMagick Q16 version of ImageMagick permits you to read and write 16 bit images without scaling but the pixel cache consumes twice as much resources as the Q8 version. If your system has constrained memory or disk resources, consider the Q8 version of ImageMagick. In addition, the Q8 version typically executes faster than the Q16 version.</p>
430
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]431<p>A great majority of image formats and algorithms restrict themselves to a fixed range of pixel values from 0 to some maximum value, for example, the Q16 version of ImageMagick permit intensities from 0 to 65535. High dynamic-range imaging (HDRI), however, permits a far greater dynamic range of exposures (i.e. a large difference between light and dark areas) than standard digital imaging techniques. HDRI accurately represents the wide range of intensity levels found in real scenes ranging from the brightest direct sunlight to the deepest darkest shadows. Enable <a href="../www/high-dynamic-range.html">HDRI</a> at ImageMagick build time to deal with high dynamic-range images, but be mindful that each pixel component is a 32-bit floating point value. In addition, pixel values are not clamped by default so some algorithms may perform differently than the non-HDRI version.</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]432
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]433<p>If you are dealing with large images, make sure the pixel cache is written to a disk area with plenty of free space. Under Unix, this is typically <kbd>/tmp</kbd> and for Windows, <kbd>c:/temp</kbd>. You can tell ImageMagick to write the pixel cache to an alternate location with the MAGICK_TEMPORARY_PATH environment variable. For example,</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]434
cristy739df912009-10-24 16:10:18 +0000[diff] [blame]435<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>export MAGICK_TEMPORARY_PATH=/data/magick</span></p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]436
437<p>If you plan on processing the same image many times, consider the MPC format. Reading a MPC image has near-zero overhead because its in the native pixel cache format eliminating the need for decoding the image pixels. Here is an example:</p>
438
439<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.tif image.mpc</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.mpc -crop 100x100+0+0 +repage 1.png</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.mpc -crop 100x100+100+0 +repage 2.png</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.mpc -crop 100x100+200+0 +repage 3.png</span></p>
440<p>MPC is ideal for web sites. It reduces the overhead of reading and writing an image. We use it exclusively at our <a href="http://www.imagemagick.org/MagickStudio/scripts/MagickStudio.cgi">online image studio</a>.</p>
441</div>
442
443</div>
444
445<h2><a name="stream"></a>Streaming Pixels</h2>
446<div class="doc-section">
447
448<p>ImageMagick provides for streaming pixels as they are read from or written to an image. This has several advantages over the pixel cache. The time and resources consumed by the pixel cache scale with the area of an image, whereas the pixel stream resources scale with the width of an image. The disadvantage is the pixels must be consumed as they are streamed so there is no persistence.</p>
449
450<p>Use <a href="../www/api/stream.html#ReadStream">ReadStream()</a> or <a href="../www/api/stream.html#WriteStream">WriteStream()</a> with an appropriate callback method in your MagickCore program to consume the pixels as they are streaming. Here's an abbreviated example of using ReadStream:</p>
451
452<pre class="code">
453static size_t StreamHandler(const Image *image,const void *pixels,
454 const size_t columns)
455{
456 /* process pixels here */
457 return(columns);
458}
459
460...
461/* invoke the pixel stream here */
462image=ReadStream(image_info,&amp;StreamHandler,exception);
463</pre>
464
465<p>We also provide a lightweight tool, <a name="stream"></a><a href="../www/stream.html">stream</a>, to stream one or more pixel components of the image or portion of the image to your choice of storage formats. It writes the pixel components as they are read from the input image a row at a time making <a name="stream"></a><a href="../www/stream.html">stream</a> desirable when working with large images or when you require raw pixel components.</p>
466
467</div>
468
469<h2><a name="properties"></a>Image Properties and Profiles</h2>
470<div class="doc-section">
471
472<p>Images have metadata associated with them in the form of properties (e.g. width, height, description, etc.) and profiles (e.g. EXIF, IPTC, color management). ImageMagick provides convenient methods to get, set, or update image properties and get, set, update, or apply profiles. Some of the more popular image properties are associated with the Image structure in the MagickCore API. For example:</p>
473
474<pre class="code">
475 (void) printf("image width: %lu, height: %lu\n",image-&gt;columns,image-&gt;rows);
476</pre>
477
478<p>For a great majority of image properties, such as an image comment or description, we use the <a href="../www/api/property.html#GetImageProperty">GetImageProperty()</a> and <a href="../www/api/property.html#SetImageProperty">SetImageProperty()</a> methods. Here we set a property and fetch it right back:</p>
479
480<pre class="code">
481 const char
482 *comment;
483
484 (void) SetImageProperty(image,"comment","This space for rent");
485 comment=GetImageProperty(image,"comment");
486 if (comment == (const char *) NULL)
487 (void) printf("Image comment: %s\n",comment);
488</pre>
489
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]490<p>ImageMagick supports artifacts with the GetImageArtifact() and SetImageArtifact() methods. Artifacts are stealth properties that are not exported to image formats (e.g. PNG) and they do not display when identifying an image.</p>
491
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]492<p>Image profiles are handled with <a href="../www/api/profile.html#GetImageProfile">GetImageProfile()</a>, <a href="../www/api/profile.html#SetImageProfile">SetImageProfile()</a>, and <a href="../www/api/profile.html#ProfileImage">ProfileImage()</a> methods. Here we set a profile and fetch it right back:</p>
493
494<pre class="code">
495 StringInfo
496 *profile;
497
498 profile=AcquireStringInfo(length);
499 SetStringInfoDatum(profile,my_exif_profile);
500 (void) SetImageProfile(image,"EXIF",profile);
501 DestroyStringInfo(profile);
502 profile=GetImageProfile(image,"EXIF");
503 if (profile != (StringInfo *) NULL)
504 (void) PrintStringInfo(stdout,"EXIF",profile);
505</pre>
506
507</div>
508
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]509<h2><a name="tera-pixel"></a>Large Image Support</h2>
510<div class="doc-section">
511<p>ImageMagick can read, process, or write mega-, giga-, or tera-pixel image sizes. For example, here we resize an image to a quarter million pixels square:</p>
512
513<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert logo: -resize 250000x250000 logo.miff</span></p>
514<p>For large images, ImageMagick will more than likely create a pixel cache on disk. Make sure you have plenty of temporary disk space. If your default temporary disk partition is too small, tell ImageMagick to use another partition with plenty of free space. For example:</p>
515
516<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp logo: -resize 250000x250000 logo.miff</span></p>
517<p>To ensure large images do not consume all the memory on your system, force the image pixels to memory-mapped disk with resource limits:</p>
518
519<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp -limit memory 16mb logo: -resize 250000x250000 logo.miff</span></p>
520<p>Here we force all image pixels to disk:</p>
521
522<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -define registry:temporary-path=/data/tmp -limit area 0 logo: -resize 250000x250000 logo.miff</span></p>
523<p>Caching pixels to disk is about 1000 times slower than memory. Expect long run times when processing large images with ImageMagick. You can monitor progress with this command:</p>
524
525<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert -monitor -define registry:temporary-path=/data/tmp -limit area 0 logo: -resize 250000x250000 logo.miff</span></p></div>
526
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]527<h2><a name="threads"></a>Threads of Execution</h2>
528<div class="doc-section">
529
530<p>Many of ImageMagick's internal algorithms are threaded to take advantage of speed-ups offered by the dual and quad-core processor technologies. However, you are welcome to use ImageMagick algorithms in your threads of execution with the exception of the MagickCore's GetVirtualPixels(), GetAuthenticPixels(), QueueAuthenticPixels(), or SyncAuthenticPixels() pixel cache methods. These methods are intended for one thread of execution only. To access the pixel cache with more than one thread of execution, use a cache view. We do this for the <a href="../www/api/composite.html#CompositeImage">CompositeImage()</a> method, for example. Suppose we want to composite a single image over a different image in each thread of execution. If we use GetVirtualPixels(), the results are unpredictable because multiple threads would likely be asking for different areas of the pixel cache simultaneously. Instead we use GetCacheViewVirtualPixels() which creates a unique view for each thread of execution ensuring our program behaves properly regardless of how many threads are invoked. The other program interfaces, such as the <a href="../www/magick-wand.html">MagickWand API</a>, are completely thread safe so there are no special precautions for threads of execution.</p>
531
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]532<p>Here is an example of how ImageMagick can take advantage of threads of execution with the <a href="http://en.wikipedia.org/wiki/OpenMP">OpenMP</a> programming paradigm:</p>
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]533
534<div class="viewport">
535<pre class="code">
536{
537 CacheView
538 *image_view;
539
540 long
541 y;
542
543 MagickBooleanType
544 status;
545
546 status=MagickTrue;
547 image_view=AcquireCacheView(image);
548 #pragma omp parallel for schedule(dynamic,4) shared(status)
549 for (y=0; y &lt; (long) image-&gt;rows; y++)
550 {
551 register IndexPacket
552 *indexes;
553
554 register long
555 x;
556
557 register PixelPacket
558 *q;
559
560 if (status == MagickFalse)
561 continue;
562 q=GetCacheViewAuthenticPixels(image_view,0,y,image-&gt;columns,1,exception);
563 if (q == (PixelPacket *) NULL)
564 {
565 status=MagickFalse;
566 continue;
567 }
568 indexes=GetCacheViewAuthenticIndexQueue(image_view);
569 for (x=0; x &lt; (long) image-&gt;columns; x++)
570 {
571 q-&gt;red= ...
572 q-&gt;green= ...
573 q-&gt;blue= ...
574 q-&gt;opacity= ...
575 if (indexes != (IndexPacket *) NULL)
576 indexes[x]= ...
577 q++;
578 }
579 if (SyncCacheViewAuthenticPixels(image_view,exception) == MagickFalse)
580 status=MagickFalse;
581 }
582 image_view=DestroyCacheView(image_view);
583 if (status == MagickFalse)
584 perror("something went wrong");
585}
586</pre>
587</div>
588
589<p>If you call the ImageMagick API from your OpenMP-enabled application and you intend to dynamically increase the number of threads available in subsequent parallel regions, be sure to perform the increase <em>before</em> you call the API otherwise ImageMagick may fault.</p>
590
591</div>
592
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]593<h2><a name="distributed"></a>Heterogeneous Distributed Processing</h2>
594<div class="doc-section">
595<p>ImageMagick includes support for heterogeneous distributed processing with the <a href="http://en.wikipedia.org/wiki/OpenCL">OpenCL</a> framework. OpenCL kernels within ImageMagick permit image processing algorithms to execute across heterogeneous platforms consisting of CPUs, GPUs, and other processors. Depending on your platform, speed-ups can be an order of magnitude faster than the traditional single CPU.</p>
596
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]597<p>First verify that your version of ImageMagick includes support for the OpenCL feature:</p>
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]598
cristyd43a46b2010-01-21 02:13:41 +0000[diff] [blame]599<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>identify -version</span><span class='crtout'>Features: OpenMP OpenCL</span></p>
600<p>If so, run this command to realize a significant speed-up for image convolution:</p>
601
602<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert image.png convolve '-1, -1, -1, -1, 9, -1, -1, -1, -1' convolve.png</span></p>
603<p>If an accelerator is not available or if the accelerator fails to respond, ImageMagick reverts to the non-accelerated convolution algorithm.</p>
604
cristy16ff93c2010-01-13 23:18:07 +0000[diff] [blame]605<p>Here is an example OpenCL kernel that convolves an image:</p>
606
607<div class="viewport">
608<pre class="code">
609static inline long ClampToCanvas(const long offset,const ulong range)
610{
611 if (offset &lt; 0L)
612 return(0L);
613 if (offset >= range)
614 return((long) (range-1L));
615 return(offset);
616}
617
618static inline CLQuantum ClampToQuantum(const double value)
619{
620 if (value &lt; 0.0)
621 return((CLQuantum) 0);
622 if (value >= (double) QuantumRange)
623 return((CLQuantum) QuantumRange);
624 return((CLQuantum) (value+0.5));
625}
626
627__kernel void Convolve(const __global CLPixelType *source,__constant double *filter,
628 const ulong width,const ulong height,__global CLPixelType *destination)
629{
630 const ulong columns = get_global_size(0);
631 const ulong rows = get_global_size(1);
632
633 const long x = get_global_id(0);
634 const long y = get_global_id(1);
635
636 const double scale = (1.0/QuantumRange);
637 const long mid_width = (width-1)/2;
638 const long mid_height = (height-1)/2;
639 double4 sum = { 0.0, 0.0, 0.0, 0.0 };
640 double gamma = 0.0;
641 register ulong i = 0;
642
643 for (long v=(-mid_height); v &lt;= mid_height; v++)
644 {
645 for (long u=(-mid_width); u &lt;= mid_width; u++)
646 {
647 register const ulong index=ClampToCanvas(y+v,rows)*columns+ClampToCanvas(x+u,columns);
648 const double alpha=scale*(QuantumRange-source[index].w);
649 sum.x+=alpha*filter[i]*source[index].x;
650 sum.y+=alpha*filter[i]*source[index].y;
651 sum.z+=alpha*filter[i]*source[index].z;
652 sum.w+=filter[i]*source[index].w;
653 gamma+=alpha*filter[i];
654 i++;
655 }
656 }
657
658 gamma=1.0/(fabs(gamma) &lt;= MagickEpsilon ? 1.0 : gamma);
659 const ulong index=y*columns+x;
660 destination[index].x=ClampToQuantum(gamma*sum.x);
661 destination[index].y=ClampToQuantum(gamma*sum.y);
662 destination[index].z=ClampToQuantum(gamma*sum.z);
663 destination[index].w=ClampToQuantum(sum.w);
664};
665</pre>
666</div>
667
668<p>See <a href="http://trac.imagemagick.org/browser/ImageMagick/trunk/filters/convolve.c">filters/convolve.c</a> for a complete implementation of image convolution with an OpenCL kernel.</p>
669
670</div>
671
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]672<h2><a name="coders"></a>Custom Image Coders</h2>
673<div class="doc-section">
674
675<p>An image coder (i.e. encoder / decoder) is responsible for registering, optionally classifying, optionally reading, optionally writing, and unregistering one image format (e.g. PNG, GIF, JPEG, etc.). Registering an image coder alerts ImageMagick a particular format is available to read or write. While unregistering tells ImageMagick the format is no longer available. The classifying method looks at the first few bytes of an image and determines if the image is in the expected format. The reader sets the image size, colorspace, and other properties and loads the pixel cache with the pixels. The reader returns a single image or an image sequence (if the format supports multiple images per file), or if an error occurs, an exception and a null image. The writer does the reverse. It takes the image properties and unloads the pixel cache and writes them as required by the image format.</p>
676
677<p>Here is a listing of a sample <a href="../www/source/mgk.c">custom coder</a>. It reads and writes images in the MGK image format which is simply an ID followed by the image width and height followed by the RGB pixel values.</p>
678
679<div class="viewport">
680<pre class="code">
681/*
682 Include declarations.
683*/
684#include "magick/studio.h"
685#include "magick/blob.h"
686#include "magick/blob-private.h"
687#include "magick/colorspace.h"
688#include "magick/exception.h"
689#include "magick/exception-private.h"
690#include "magick/image.h"
691#include "magick/image-private.h"
692#include "magick/list.h"
693#include "magick/magick.h"
694#include "magick/memory_.h"
695#include "magick/monitor.h"
696#include "magick/monitor-private.h"
697#include "magick/quantum-private.h"
698#include "magick/static.h"
699#include "magick/string_.h"
700#include "magick/module.h"
701
702/*
703 Forward declarations.
704*/
705static MagickBooleanType
706 WriteMGKImage(const ImageInfo *,Image *);
707
708/*
709%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
710% %
711% %
712% %
713% I s M G K %
714% %
715% %
716% %
717%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
718%
719% IsMGK() returns MagickTrue if the image format type, identified by the
720% magick string, is MGK.
721%
722% The format of the IsMGK method is:
723%
724% MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
725%
726% A description of each parameter follows:
727%
728% o magick: This string is generally the first few bytes of an image file
729% or blob.
730%
731% o length: Specifies the length of the magick string.
732%
733*/
734static MagickBooleanType IsMGK(const unsigned char *magick,const size_t length)
735{
736 if (length &lt; 7)
737 return(MagickFalse);
738 if (LocaleNCompare((char *) magick,"id=mgk",7) == 0)
739 return(MagickTrue);
740 return(MagickFalse);
741}
742
743/*
744%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
745% %
746% %
747% %
748% R e a d M G K I m a g e %
749% %
750% %
751% %
752%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
753%
754% ReadMGKImage() reads a MGK image file and returns it. It allocates
755% the memory necessary for the new Image structure and returns a pointer to
756% the new image.
757%
758% The format of the ReadMGKImage method is:
759%
760% Image *ReadMGKImage(const ImageInfo *image_info,ExceptionInfo *exception)
761%
762% A description of each parameter follows:
763%
764% o image_info: the image info.
765%
766% o exception: return any errors or warnings in this structure.
767%
768*/
769static Image *ReadMGKImage(const ImageInfo *image_info,
770 ExceptionInfo *exception)
771{
772 char
773 buffer[MaxTextExtent];
774
775 Image
776 *image;
777
778 long
779 y;
780
781 MagickBooleanType
782 status;
783
784 register long
785 x;
786
787 register PixelPacket
788 *q;
789
790 register unsigned char
791 *p;
792
793 ssize_t
794 count;
795
796 unsigned char
797 *pixels;
798
799 unsigned long
800 columns,
801 rows;
802
803 /*
804 Open image file.
805 */
806 assert(image_info != (const ImageInfo *) NULL);
807 assert(image_info-&gt;signature == MagickSignature);
808 if (image_info-&gt;debug != MagickFalse)
809 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image_info-&gt;filename);
810 assert(exception != (ExceptionInfo *) NULL);
811 assert(exception-&gt;signature == MagickSignature);
812 image=AcquireImage(image_info);
813 status=OpenBlob(image_info,image,ReadBinaryBlobMode,exception);
814 if (status == MagickFalse)
815 {
816 image=DestroyImageList(image);
817 return((Image *) NULL);
818 }
819 /*
820 Read MGK image.
821 */
822 (void) ReadBlobString(image,buffer); /* read magic number */
823 if (IsMGK(buffer,7) == MagickFalse)
824 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
825 (void) ReadBlobString(image,buffer);
826 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
827 if (count &lt;= 0)
828 ThrowReaderException(CorruptImageError,"ImproperImageHeader");
829 do
830 {
831 /*
832 Initialize image structure.
833 */
834 image-&gt;columns=columns;
835 image-&gt;rows=rows;
836 image-&gt;depth=8;
837 if ((image_info-&gt;ping != MagickFalse) &amp;&amp; (image_info-&gt;number_scenes != 0))
838 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
839 break;
840 /*
841 Convert MGK raster image to pixel packets.
842 */
843 if (SetImageExtent(image,0,0) == MagickFalse)
844 {
845 InheritException(exception,&amp;image-&gt;exception);
846 return(DestroyImageList(image));
847 }
848 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,3UL*sizeof(*pixels));
849 if (pixels == (unsigned char *) NULL)
850 ThrowReaderException(ResourceLimitError,"MemoryAllocationFailed");
851 for (y=0; y &lt; (long) image-&gt;rows; y++)
852 {
853 count=(ssize_t) ReadBlob(image,(size_t) (3*image-&gt;columns),pixels);
854 if (count != (ssize_t) (3*image-&gt;columns))
855 ThrowReaderException(CorruptImageError,"UnableToReadImageData");
856 p=pixels;
857 q=QueueAuthenticPixels(image,0,y,image-&gt;columns,1,exception);
858 if (q == (PixelPacket *) NULL)
859 break;
860 for (x=0; x &lt; (long) image-&gt;columns; x++)
861 {
862 q-&gt;red=ScaleCharToQuantum(*p++);
863 q-&gt;green=ScaleCharToQuantum(*p++);
864 q-&gt;blue=ScaleCharToQuantum(*p++);
865 q++;
866 }
867 if (SyncAuthenticPixels(image,exception) == MagickFalse)
868 break;
869 if ((image-&gt;previous == (Image *) NULL) &&
870 (SetImageProgress(image,LoadImageTag,y,image&gt;>rows) == MagickFalse))
871 break;
872 }
873 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
874 if (EOFBlob(image) != MagickFalse)
875 {
876 ThrowFileException(exception,CorruptImageError,"UnexpectedEndOfFile",image-&gt;filename);
877 break;
878 }
879 /*
880 Proceed to next image.
881 */
882 if (image_info-&gt;number_scenes != 0)
883 if (image-&gt;scene >= (image_info-&gt;scene+image_info-&gt;number_scenes-1))
884 break;
885 *buffer='\0';
886 (void) ReadBlobString(image,buffer);
887 count=(ssize_t) sscanf(buffer,"%lu %lu\n",&amp;columns,&amp;rows);
888 if (count != 0)
889 {
890 /*
891 Allocate next image structure.
892 */
893 AcquireNextImage(image_info,image);
894 if (GetNextImageInList(image) == (Image *) NULL)
895 {
896 image=DestroyImageList(image);
897 return((Image *) NULL);
898 }
899 image=SyncNextImageInList(image);
900 status=SetImageProgress(image,LoadImageTag,TellBlob(image),GetBlobSize(image));
901 if (status == MagickFalse)
902 break;
903 }
904 } while (count != 0);
905 (void) CloseBlob(image);
906 return(GetFirstImageInList(image));
907}
908
909/*
910%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
911% %
912% %
913% %
914% R e g i s t e r M G K I m a g e %
915% %
916% %
917% %
918%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
919%
920% RegisterMGKImage() adds attributes for the MGK image format to
921% the list of supported formats. The attributes include the image format
922% tag, a method to read and/or write the format, whether the format
923% supports the saving of more than one frame to the same file or blob,
924% whether the format supports native in-memory I/O, and a brief
925% description of the format.
926%
927% The format of the RegisterMGKImage method is:
928%
929% unsigned long RegisterMGKImage(void)
930%
931*/
932ModuleExport unsigned long RegisterMGKImage(void)
933{
934 MagickInfo
935 *entry;
936
937 entry=SetMagickInfo("MGK");
938 entry-&gt;decoder=(DecodeImageHandler *) ReadMGKImage;
939 entry-&gt;encoder=(EncodeImageHandler *) WriteMGKImage;
940 entry-&gt;magick=(IsImageFormatHandler *) IsMGK;
941 entry-&gt;description=ConstantString("MGK");
942 entry-&gt;module=ConstantString("MGK");
943 (void) RegisterMagickInfo(entry);
944 return(MagickImageCoderSignature);
945}
946
947/*
948%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
949% %
950% %
951% %
952% U n r e g i s t e r M G K I m a g e %
953% %
954% %
955% %
956%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
957%
958% UnregisterMGKImage() removes format registrations made by the
959% MGK module from the list of supported formats.
960%
961% The format of the UnregisterMGKImage method is:
962%
963% UnregisterMGKImage(void)
964%
965*/
966ModuleExport void UnregisterMGKImage(void)
967{
968 (void) UnregisterMagickInfo("MGK");
969}
970
971/*
972%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
973% %
974% %
975% %
976% W r i t e M G K I m a g e %
977% %
978% %
979% %
980%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
981%
982% WriteMGKImage() writes an image to a file in red, green, and blue
983% MGK rasterfile format.
984%
985% The format of the WriteMGKImage method is:
986%
987% MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
988%
989% A description of each parameter follows.
990%
991% o image_info: the image info.
992%
993% o image: The image.
994%
995*/
996static MagickBooleanType WriteMGKImage(const ImageInfo *image_info,Image *image)
997{
998 char
999 buffer[MaxTextExtent];
1000
1001 long
1002 y;
1003
1004 MagickBooleanType
1005 status;
1006
1007 MagickOffsetType
1008 scene;
1009
1010 register const PixelPacket
1011 *p;
1012
1013 register long
1014 x;
1015
1016 register unsigned char
1017 *q;
1018
1019 unsigned char
1020 *pixels;
1021
1022 /*
1023 Open output image file.
1024 */
1025 assert(image_info != (const ImageInfo *) NULL);
1026 assert(image_info-&gt;signature == MagickSignature);
1027 assert(image != (Image *) NULL);
1028 assert(image-&gt;signature == MagickSignature);
1029 if (image-&gt;debug != MagickFalse)
1030 (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",image-&gt;filename);
1031 status=OpenBlob(image_info,image,WriteBinaryBlobMode,&amp;image-&gt;exception);
1032 if (status == MagickFalse)
1033 return(status);
1034 scene=0;
1035 do
1036 {
1037 /*
1038 Allocate memory for pixels.
1039 */
1040 if (image-&gt;colorspace != RGBColorspace)
1041 (void) SetImageColorspace(image,RGBColorspace);
1042 pixels=(unsigned char *) AcquireQuantumMemory((size_t) image-&gt;columns,
1043 3UL*sizeof(*pixels));
1044 if (pixels == (unsigned char *) NULL)
1045 ThrowWriterException(ResourceLimitError,"MemoryAllocationFailed");
1046 /*
1047 Initialize raster file header.
1048 */
1049 (void) WriteBlobString(image,"id=mgk\n");
1050 (void) FormatMagickString(buffer,MaxTextExtent,"%lu %lu\n",
1051 image-&gt;columns,image-&gt;rows);
1052 (void) WriteBlobString(image,buffer);
1053 for (y=0; y &lt; (long) image-&gt;rows; y++)
1054 {
1055 p=GetVirtualPixels(image,0,y,image-&gt;columns,1,&amp;image-&gt;exception);
1056 if (p == (const PixelPacket *) NULL)
1057 break;
1058 q=pixels;
1059 for (x=0; x &lt; (long) image-&gt;columns; x++)
1060 {
1061 *q++=ScaleQuantumToChar(p-&gt;red);
1062 *q++=ScaleQuantumToChar(p-&gt;green);
1063 *q++=ScaleQuantumToChar(p-&gt;blue);
1064 p++;
1065 }
1066 (void) WriteBlob(image,(size_t) (q-pixels),pixels);
1067 if ((image-&gt;previous == (Image *) NULL) &&
1068 (SetImageProgress(image,SaveImageTag,y,image-&gt;rows) == MagickFalse))
1069 break;
1070 }
1071 pixels=(unsigned char *) RelinquishMagickMemory(pixels);
1072 if (GetNextImageInList(image) == (Image *) NULL)
1073 break;
1074 image=SyncNextImageInList(image);
1075 status=SetImageProgress(image,SaveImagesTag,scene,
1076 GetImageListLength(image));
1077 if (status == MagickFalse)
1078 break;
1079 scene++;
1080 } while (image_info-&gt;adjoin != MagickFalse);
1081 (void) CloseBlob(image);
1082 return(MagickTrue);
1083}
1084</pre>
1085</div>
1086
1087<p>To invoke the custom coder from the command line, use these commands:</p>
1088
1089<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert logo: logo.mgk</span><span class='crtout'></span><span class="crtprompt"> $magick&gt; </span><span class='crtin'>display logo.mgk</span></p>
1090<p>We provide the <a href="ftp://ftp.imagemagick.org/pub/ImageMagick/kits/MagickCoderKit-1.0.0.tar.gz">Magick Coder Kit</a> to help you get started writing your own custom coder.</p>
1091
1092</div>
1093
1094<h2><a name="filters"></a>Custom Image Filters</h2>
1095<div class="doc-section">
1096
1097<p>ImageMagick provides a convenient mechanism for adding your own custom image processing algorithms. We call these image filters and they are invoked from the command line with the <a href="../www/command-line-options.html#process">-process</a> option or from the MagickCore API method <a href="../www/api/module.html#ExecuteModuleProcess">ExecuteModuleProcess()</a>.</p>
1098
1099<p>Here is a listing of a sample <a href="../www/source/analyze.c">custom image filter</a>. It computes a few statistics such as the pixel brightness and saturation mean and standard-deviation.</p>
1100
1101<div class="viewport">
1102<pre class="code">
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1103#include &lt;stdio.h&gt;
1104#include &lt;stdlib.h&gt;
1105#include &lt;string.h&gt;
1106#include &lt;time.h&gt;
1107#include &lt;assert.h&gt;
1108#include &lt;math.h&gt;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1109#include "magick/MagickCore.h"
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1110
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1111/*
1112%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1113% %
1114% %
1115% %
1116% a n a l y z e I m a g e %
1117% %
1118% %
1119% %
1120%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
1121%
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1122% analyzeImage() computes the brightness and saturation mean, standard
1123% deviation, kurtosis and skewness and stores these values as attributes
1124% of the image.
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1125%
1126% The format of the analyzeImage method is:
1127%
1128% unsigned long analyzeImage(Image *images,const int argc,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1129% char **argv,ExceptionInfo *exception)
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1130%
1131% A description of each parameter follows:
1132%
1133% o image: the address of a structure of type Image.
1134%
1135% o argc: Specifies a pointer to an integer describing the number of
1136% elements in the argument vector.
1137%
1138% o argv: Specifies a pointer to a text array containing the command line
1139% arguments.
1140%
1141% o exception: return any errors or warnings in this structure.
1142%
1143*/
1144ModuleExport unsigned long analyzeImage(Image **images,const int argc,
1145 const char **argv,ExceptionInfo *exception)
1146{
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1147 char
1148 text[MaxTextExtent];
1149
1150 double
1151 area,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1152 brightness,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1153 brightness_mean,
1154 brightness_standard_deviation,
1155 brightness_kurtosis,
1156 brightness_skewness,
1157 brightness_sum_x,
1158 brightness_sum_x2,
1159 brightness_sum_x3,
1160 brightness_sum_x4,
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1161 hue,
1162 saturation,
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1163 saturation_mean,
1164 saturation_standard_deviation,
1165 saturation_kurtosis,
1166 saturation_skewness,
1167 saturation_sum_x,
1168 saturation_sum_x2,
1169 saturation_sum_x3,
1170 saturation_sum_x4;
1171
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1172 Image
1173 *image;
1174
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1175 assert(images != (Image **) NULL);
1176 assert(*images != (Image *) NULL);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1177 assert((*images)-&gt;signature == MagickSignature);
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1178 (void) argc;
1179 (void) argv;
1180 image=(*images);
1181 for ( ; image != (Image *) NULL; image=GetNextImageInList(image))
1182 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1183 CacheView
1184 *image_view;
1185
1186 long
1187 y;
1188
1189 MagickBooleanType
1190 status;
1191
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1192 brightness_sum_x=0.0;
1193 brightness_sum_x2=0.0;
1194 brightness_sum_x3=0.0;
1195 brightness_sum_x4=0.0;
1196 brightness_mean=0.0;
1197 brightness_standard_deviation=0.0;
1198 brightness_kurtosis=0.0;
1199 brightness_skewness=0.0;
1200 saturation_sum_x=0.0;
1201 saturation_sum_x2=0.0;
1202 saturation_sum_x3=0.0;
1203 saturation_sum_x4=0.0;
1204 saturation_mean=0.0;
1205 saturation_standard_deviation=0.0;
1206 saturation_kurtosis=0.0;
1207 saturation_skewness=0.0;
1208 area=0.0;
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1209 status=MagickTrue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1210 image_view=AcquireCacheView(image);
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1211#if defined(MAGICKCORE_OPENMP_SUPPORT)
1212 #pragma omp parallel for schedule(dynamic,4) shared(status)
1213#endif
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1214 for (y=0; y &lt; (long) image-&gt;rows; y++)
1215 {
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1216 register const PixelPacket
1217 *p;
1218
1219 register long
1220 x;
1221
1222 if (status == MagickFalse)
1223 continue;
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1224 p=GetCacheViewVirtualPixels(image_view,0,y,image-&gt;columns,1,exception);
1225 if (p == (const PixelPacket *) NULL)
cristy76e378e2009-12-21 18:20:04 +0000[diff] [blame]1226 {
1227 status=MagickFalse;
1228 continue;
1229 }
cristy3ed852e2009-09-05 21:47:34 +0000[diff] [blame]1230 for (x=0; x &lt; (long) image-&gt;columns; x++)
1231 {
1232 ConvertRGBToHSB(p-&gt;red,p-&gt;green,p-&gt;blue,&amp;hue,&amp;saturation,&amp;brightness);
1233 brightness*=QuantumRange;
1234 brightness_sum_x+=brightness;
1235 brightness_sum_x2+=brightness*brightness;
1236 brightness_sum_x3+=brightness*brightness*brightness;
1237 brightness_sum_x4+=brightness*brightness*brightness*brightness;
1238 saturation*=QuantumRange;
1239 saturation_sum_x+=saturation;
1240 saturation_sum_x2+=saturation*saturation;
1241 saturation_sum_x3+=saturation*saturation*saturation;
1242 saturation_sum_x4+=saturation*saturation*saturation*saturation;
1243 area++;
1244 p++;
1245 }
1246 }
1247 image_view=DestroyCacheView(image_view);
1248 if (area &lt;= 0.0)
1249 break;
1250 brightness_mean=brightness_sum_x/area;
1251 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_mean);
1252 (void) SetImageProperty(image,"filter:brightness:mean",text);
1253 brightness_standard_deviation=sqrt(brightness_sum_x2/area-(brightness_sum_x/
1254 area*brightness_sum_x/area));
1255 (void) FormatMagickString(text,MaxTextExtent,"%g",
1256 brightness_standard_deviation);
1257 (void) SetImageProperty(image,"filter:brightness:standard-deviation",text);
1258 if (brightness_standard_deviation != 0)
1259 brightness_kurtosis=(brightness_sum_x4/area-4.0*brightness_mean*
1260 brightness_sum_x3/area+6.0*brightness_mean*brightness_mean*
1261 brightness_sum_x2/area-3.0*brightness_mean*brightness_mean*
1262 brightness_mean*brightness_mean)/(brightness_standard_deviation*
1263 brightness_standard_deviation*brightness_standard_deviation*
1264 brightness_standard_deviation)-3.0;
1265 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_kurtosis);
1266 (void) SetImageProperty(image,"filter:brightness:kurtosis",text);
1267 if (brightness_standard_deviation != 0)
1268 brightness_skewness=(brightness_sum_x3/area-3.0*brightness_mean*
1269 brightness_sum_x2/area+2.0*brightness_mean*brightness_mean*
1270 brightness_mean)/(brightness_standard_deviation*
1271 brightness_standard_deviation*brightness_standard_deviation);
1272 (void) FormatMagickString(text,MaxTextExtent,"%g",brightness_skewness);
1273 (void) SetImageProperty(image,"filter:brightness:skewness",text);
1274 saturation_mean=saturation_sum_x/area;
1275 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_mean);
1276 (void) SetImageProperty(image,"filter:saturation:mean",text);
1277 saturation_standard_deviation=sqrt(saturation_sum_x2/area-(saturation_sum_x/
1278 area*saturation_sum_x/area));
1279 (void) FormatMagickString(text,MaxTextExtent,"%g",
1280 saturation_standard_deviation);
1281 (void) SetImageProperty(image,"filter:saturation:standard-deviation",text);
1282 if (saturation_standard_deviation != 0)
1283 saturation_kurtosis=(saturation_sum_x4/area-4.0*saturation_mean*
1284 saturation_sum_x3/area+6.0*saturation_mean*saturation_mean*
1285 saturation_sum_x2/area-3.0*saturation_mean*saturation_mean*
1286 saturation_mean*saturation_mean)/(saturation_standard_deviation*
1287 saturation_standard_deviation*saturation_standard_deviation*
1288 saturation_standard_deviation)-3.0;
1289 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_kurtosis);
1290 (void) SetImageProperty(image,"filter:saturation:kurtosis",text);
1291 if (saturation_standard_deviation != 0)
1292 saturation_skewness=(saturation_sum_x3/area-3.0*saturation_mean*
1293 saturation_sum_x2/area+2.0*saturation_mean*saturation_mean*
1294 saturation_mean)/(saturation_standard_deviation*
1295 saturation_standard_deviation*saturation_standard_deviation);
1296 (void) FormatMagickString(text,MaxTextExtent,"%g",saturation_skewness);
1297 (void) SetImageProperty(image,"filter:saturation:skewness",text);
1298 }
1299 return(MagickImageFilterSignature);
1300}
1301</pre>
1302</div>
1303
1304<p>To invoke the custom filter from the command line, use this command:</p>
1305
1306<p class='crt'><span class="crtprompt"> $magick&gt; </span><span class='crtin'>convert logo: -process analyze -verbose info:</span><span class='crtout'>Image: logo: <br/>
1307 Format: LOGO (ImageMagick Logo) <br/>
1308 Class: PseudoClass <br/>
1309 Geometry: 640x480 <br/>
1310 ... <br/>
1311 filter:brightness:kurtosis: 8.98864 <br/>
1312 filter:brightness:mean: 238.096 <br/>
1313 filter:brightness:skewness: -3.04519 <br/>
1314 filter:brightness:standard-deviation: 46.3286 <br/>
1315 filter:saturation:kurtosis: 5.9137 <br/>
1316 filter:saturation:mean: 23.4635 <br/>
1317 filter:saturation:skewness: 2.71874 <br/>
1318 filter:saturation:standard-deviation: 64.7734</span></p>
1319
1320<p>We provide the <a href="ftp://ftp.imagemagick.org/pub/ImageMagick/kits/MagickFilterKit-1.0.0.tar.gz">Magick Filter Kit</a> to help you get started writing your own custom image filter.</p>
1321
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cristyf3bb4782009-09-08 13:10:04 +0000[diff] [blame]1323
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